Lithographic printing ink and the method of making the same



Patented July 20, 1943 LITHOGRAPHIC PRINTING INK AND THE I METHOD OF MAKING THE SAME Herbert J. Woii'e, Maspeth, Long Island, N. Y., as-

signor to American Can Company, New York, N. Y., a corporation of New Jersey No Drawing- Al pllcation March 8, 1939, Serial No. 260,657

5 Claims.

' which insures a printed surface more easily and quickly dried.

Printing and lithographing inks are composed essentially of pigments and vehicles. The vehicle portion of the ink which usually consists of oleoresinous materials, synthetic resins or semi-synthetic resins, is made up of various proportions of oils, resins and solvents each having its own distinct purpose. The oil imparts flexibility and permits the printing of surfaces which may be bent or flexed into different shapes. imparts hardness and gloss and insures permanency and improved appearance of the printed surface. The solvent is used to impart fluidity and is a manufacturing advantage in the mixing and preparation of many kinds and types of ink. In the present invention the alkyl phosphate solvent used imparts properties to printing and especially lithographic inks (for printing on metal surfaces, such as tin sheets) which are both important and unique.

The present invention contemplates an improvement in the art of printing by the use of an ink in which the solvent used possesses'increased quick drying solvent wetting powers so that less solvent is needed and the ink maybe made with a higher percentage of solid contents in the vehicle or in the pigments or in both, giving an ink film of better color strength, opacity. hardness, tenacious adhesion. non-skinning etc., and the ink mass may be dried in much less time than is usual in work of this kind.

In modern high speed mass production of printing, the drying of the ink is eilected by driving off the solvent usually by heat. In printing on paper, fabrics, etc., absorption plays an important role and there are also inks used for certain purposes which contain no solvents in the usually accepted sense. Thus drying may be the result of evaporation, oxidation, heat penetration, polymerization, gellation. or a combination of two or more such actions. Therefore, reduction of drying time is all important.

In the present embodiment of the invention alkyl phosphates are used primarily as a quick drying solvent and incidentally as a wetting agent and many important results follow from The resin.

such a use. The mixing of alkyl phosphates with other materials lowers the viscosity of the final product and permits the use of a higher solid percentage. Rapid drying is one such result. The lower percentage of solvent which is needed where better wetting takes place reduces the time of drying shince there is less solvent in the film to be eliminated. Aside from this solvent phase quicker drying results from better wetting action which in its turn gives a better mixing action productive of a smoother and more adhesive ink.

There being a larger percentage of solids in the ink mass, an apparently deeper body is obtained which gives a fuller color and more opacity and the closer coverage of the surface being printed permits the use of a thinner film of ink and produces a smoother and more uniform efiect. Again the hardness of the final printed film is improved. All such desirable improvements in the printing echnique are aided by or may be attributed to he alkyl phosphate used.

The tri-alk 1 phosphates, it is believed, are best adapted for rinting and lithographic inks and accordingly ese are preferred in the present invention. A ong such phosphates may be mentioned tri-b yl phosphate, tri-ethyl phosphate and tri-prop 1 phosphate as being best to use under usual An object of the invention is the provision of a. method f producing an improved printing and lithographic ink which contains a high percentage of solids at the time of mixing and while printing, the printed film being rapidly dried preferably by heat.

Another object is the provision of a method of making such a printing ink by utilization of an agent having great solvent and wetting properties which permits the proper mixture of the ink contents so that a. maximum of color strength and opacity is obtainable in the printed film.

Still another object is the provision of a meth- 0d of p eparing printing and lithographic inks by the se of alkyl phosphates as a quick drying solvent and as a wetting agent and which alkyl phosphates substantially eliminate the use of acid in the dampening water by partially hydrolyzing to phosphoric acid.

Yet another object is the provision of an improved printing and lithographic ink containing alkyl phosphates which have the valuable properties of quick drying at an elevated temperature and are substantially non-skinning while in the shipping containers and while on the printing or lithographing press.

Numerous other objects and advantages of the invention will be apparent as it is better understood from the following description which is of a preferred embodiment thereof.

In the usual practice of manufacturing inks. the pigments and vehicles are placed in a suitable mixing device to mechanically combine the various elements. Such a mechanical mixing device may be a change-can mixer, a kneading mixer, a Banbury mixer or other similar mechanism well known in ink manufacture. This part of the conventional ink making process is a time-consuming operation as wetting by .the vehicle is resisted and retarded by the tendency of the pigment particles and also to some extent of the resinous substances to lump together or agglomcrate.

In the present method in which alkyl phosphates are used, the solvent and wetting action is so greatly improved that this mixing step, just referred to, is reduced in point of time and a smoother product results. The vehicle with which the alkyl phosphates are preferably combined functions as the liquid media for the pigment and other materials. This liquid media. containing the resin and alkyl phosphate is plasticized by a drying oil as will be more specifically pointed out hereinafter. However, the alkyl phosphates may be subsequently added at the time the carrying liquid media is combined with the pigments.

One such use of lithographic inks prepared according to the present invention is found in the manufacture of tin cans. A lithographed or printed design which will be on the outer surface of the can body after the can is made is printed on a sheet of tinplate while in the fiat and which is run through a standard baking oven to thoroughly dry the ink before the other can manufacturing steps begin. By the use of the alkyl phosphate this drying time in the ordinary oven is reduced from a total drying time of perhaps half an hour to only a few minutes or even a matter of seconds.

As an example of one manner of carrying out the method steps of ink manufacture according to the present invention and where the allqrl phosphates are used in the vehicle, the following procedure is given as producing a lithographic ink which is satisfactory for printing on metal sheets from which can bodies may be subsequent- 1y made.

In such an example twenty (20) pounds of modified phenolic resin is mixed with forty (40) pounds of raw linseed oil. This mixture is cooked to preferably about 550 degrees Fahrenheit for about forty five minutes in a standard varnish kettle. The kettle of heated mixture is then removed from the fire and the contents are allowed to cool down to preferably about 300 degrees Fahrenheit.

When at this temperature, five pounds of tributyl phosphate for example, is stirred into the mixture and the resulting mass is then allowed to cool further down to room temperature. This provides the vehicle for the ink and is ready for use at this temperature.

The next step in preparing the ink according to the example now being considered, is to take about fifty (50) pounds of the vehicle and incorporate in it forty 40) pounds of barium lake of lithol toner (dry color), ten pounds of dry aluminum hydrate and two (2) pounds of cobalt linoleate (3% metal content in linseed oil). Such a mixture should be ground until it is fine, the usual roller mill being satisfactory for this purpose. When thoroughly mixed into a smooth mass, the ink is ready for use in any suitable form of lithographic press.

The improved solvent and wetting action of the alkyl phosphates is effective as soon as it comes in contact with the solids, be they in the vehicle or in the pigment phases of the ink mixture. Such alkyl phosphates, therefore, may be added to the pigments, fillers and those materials not constituting elements in the vehicle part of the ink and the same improved solvent and wetting action follows.

It is important that the mixture be thoroughly refined, that is, made smoother and more homogenous and this refining step is the result of a proper grinding of the materials. While the usual roller mill is satisfactory for this purpose other well known types of mills such as a buhr-stone mill, the pot mill, the ball mill, pebble mill or c01- loid mill may be used. The action of refining may be carried to a greater degree of perfection when alkyl phosphates are used and a better ink is produced.

The presence of the tri-butyl phosphate in this mixture makes it possible to prepare the ink in much less time than would be required if the phosphate was not used. The wetting action of the vehicle in this case is much more thorough and a smoother ink results, this being an ink having greatly increased covering characteristics. A thinner film may be used in the printing or lithographing since the color, whatever it may be, will be more opaque.

The particular materials given above in the example cited may be widely varied and also different proportions may be used without nullifying the advantages of the resulting ink mixture. The resin suggested as a modified phenolic resin may be replaced by other resins from either the natural or synthetic groups. Satisfactory resins for this purpose may be chosen from the group comprising copal, dammar, kauri, congo or their equivalents. Other groups are the phenol-formaldehyde resins, alkyd resin, maleic anhydride resin, urea-formaldehyde, styrene or cumaroneindene resins, rosin, ester gum, chlorinated rubber or terpene resins or their equivalents. As to quantity the resin component may range as much as from to depending upon the printing conditions.

It may be mentioned at this point that certain special inks may be made in which the vehicle component is the oil and in which resin is entirely absent. Such oil inks can also be improved by the use of alkyl phosphates as above described.

Other drying oils may be substituted for the raw linseed oil given in the above example. Either raw or polymerized tung oil is satisfactory, also soya bean, perilla, fish or oiticica oils, Castor oil or dehydrated castor oil may also be mentioned as well as stilllngia, tobacco seed, and sunflower seed oils, or their equivalent. Again the quantities of drying oil may vary considerably depending upon the color of inks being made and the printing conditions. A range of /4% to 50% based on the final product will not be out of place.

The quantit of alkyl phosphate used as a wetting agent or solvent is determined by the type of ink and speed of drying desired. This quantity varies considerably for the different kinds of inks and may be as little as 341% based on the total weight of the material, or may under extreme cases be as much as 50%. The lower percentages are usually employed when the alkyl phosphate is used primarily as a wetting agent. When used as solvents the higher percentages are involved.

The rapid drying of the ink containing alkyi phosphates is due in part to the narrow boiling range of temperature of these alkyl phosphates which are immediately driven out of the film as soon as the ink reaches such temperature in the drying step. This is in contradistinction to elim inating the solvents having extended boiling range temperatures such as petroleum distillates, hydrogenated naphthas or commercial aromatic hydro-carbons so universally used in present ink manufacture and where the heat of drying must be extended over a considerable range of temperatures with extended drying time. Furthermore, the drying effect is not nearly as complete or precise as with the alkyl phosphates.

Another important advantage gained by the use of alkyl phosphates in printing and lithographic inks is that the skinning, or surface drying, of the inks in the containers or fountains of the printing presses prior to application is greatly retarded, thereby saving material and eliminating frequent wash-ups or cleaning of the printing' machine.

It is thought that the invention and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes may be made in the steps of the process described and their order of accomplishment without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the process hereinbefore described being merely a preferred embodiment thereof.

I claim:

1. The process of making a quick drying printing ink designed for application to metal and similar non-absorbent surfaces at relatively high baking temperatures, which comprises mixing a rapid drying oil of high iodine value as a plasticizer with a varnish type resin, cooking the mixture at an elevated temperature to produce a homogeneous solution, cooling the solution, adding a tri-alkyl phosphate and thoroughly mixing the same to produce a carrying vehicle, and then incorporating a color pigment in said vehicle to provide an ink of the desired color, said trialkyl phosphate functioning as a quick drying solvent having the characteristic of extremely rapid evaporation when said ink is baked at relatively high temperatures, whereby to leave a dry, hard, tenaciously adhesive, ink film on said metal surface not susceptible to smudging on contact.

2. The process'of making a quick drying lithographic ink designed for application to sheet metal and similar not absorbent surfaces at relatively high baking temperatures, which comprises mixing a rapid drying oil of high iodine value as a plasticizer with a varnish type synthetic resin, cooking the mixture at a temperature substantially in excess of 400 degrees F. to produce a homogeneous solution, partially cooling the solution, adding a tri-alkyl phosphate and thoroughly mixing the same to produce a carrying vehicle, further cooling the vehicle to substantially room temperature, and then incorporating a desired color pigment in said vehicle to provide an ink, said tri-alkyl phosphate functioning as a quick drying solvent having the characteristic of extremely rapid evaporation when said ink is baked at relatively high temperatures, whereby to leave a dry, hard, tenaciously adhesive, ink film on said sheet metal surface not susceptible to smudging on contact.

3. A quick drying printing ink for application to metal and similar non-absorbent surfaces at relatively high baking temperatures, comprising in combination: a vehicle consisting of a varnish type synthetic resin, 9. rapid drying and plasticizing oil of high iodine value and a tri-alkyl phosphate, and a color pigment incorporated in said vehicle, said tri-alkyl phosphate functioning as a solvent having the characteristic of rapid evaporation when said ink is baked at relatively high temperatures to leave a tenaciously adhesive ink film on said metal surface.

4. A quick drying printing ink for application to metal and similar non-absorbent surfaces at relatively high baking temperatures, comprising in combination: a vehicle consisting of a varnish type synthetic resin, a rapid drying and plasticizing oil of high iodine value and tri-butyl phosphate, and a color pigment incorporated in said vehicle, said tri-butyl phosphate functioning as a solvent having the characteristic of rapidevaporation when said ink is baked at relatively high temperatures to leave a tenaciously adhesive ink film on said metal surface.

5. A quick drying printing ink for application to metal and similar non-absorbent surfaces at relatively high baking temperatures, comprising in combination: a vehicle consisting of a varnish type synthetic resin, a rapid drying and plasticizing oil of high iodine value. and tri-propyl phosphate, and a color pigment incorporated in said vehicle, said tri-propyl phosphate functioning as a solvent having the characteristic of rapid evaporation when said ink is baked at relatively high temperatures to leave a tenaciously adhesive ink film on said metal surface.

HERBERT J. WOLFE. 

